Dec 27 (Reuters) - A U.S. storm system that by Thursday morning had already caused flight disruptions and blizzard-like conditions was expected to dump up to 10 inches (25 cm) of snow on some states and heavy rainfall on others, weather officials said.

Parts of the U.S. Midwest and Southeast were experiencing the first wave of heavy snow and rain expected to strike the central United States through the holiday weekend. The National Weather Service (NWS) warned on Thursday that travel will be hazardous.

In the Midwest, winter storms and blizzard warnings were already in effect for parts of Kansas, Nebraska, North Dakota, South Dakota and Minnesota, said NWS meteorologist Marc Chenard.

“Through this morning there have already been amounts as high of 6 to 10 inches across those areas and additional snowfall of 10 inches is possible throughout the day and tonight,” Chenard said. “Travel is going to be very difficult across the areas under weather and blizzard warnings.”

Chenard said the storm system was also causing heavy rain and thunderstorms with the risk of flash floods in the southeastern United States, including parts of Texas, Louisiana, Mississippi and Alabama. A tornado watch for parts of central and southwest Louisiana and southeast Texas were in effect on Thursday.

The storm, which began late on Wednesday, contributed to more than 2,300 flight delays and about 509 cancellations within, into or out of the United States by Thursday afternoon, according to FlightAware.com. There were nearly 320 cancellations at Dallas-Fort Worth International Airport in Texas.

Kansas Governor Jeff Colyer on Wednesday declared a state of emergency in response to the storm.

“It is important to be prepared when we see a winter event like this approaching,” Colyer said in a statement. “We hope that travelers will be wise by paying attention to weather alerts and not unnecessarily placing themselves in harm’s way as the storm moves through.” (Reporting by Gina Cherelus in New York Editing by Matthew Lewis)